Secondary succession: changes in relative abundance of tree species at Hubbard Brook Experimental Forest

34 invertebrate communities in streamsA, B, C, D indicate community types determined by classification

Classification

Primary succession: colonization of concrete blocks in intertidal zone by algae

Keystone species

Sea otter

urchins

kelp

Heterotrophic succession: fungal populations colonizing pine litter

No disturbance

Periodic density-dependent disturbance

Enteromorpha ChondrusPreferred food Poor food sourceDominant competitor Poor competitor

Littorina littorea

Ecosystem:

Tansley (1935)

“The more fundamental conception is… the whole ecosystem including not only the organism-complex, but also the whole complex of physical factors forming what we call the environment…

We cannot separate the organisms from their special environment with which they form one physical system….

It is the system so formed which provides the basic units of nature on the face of the earth.”

Precipitation

Temperature

temperature

Rat

e of

pho

tosy

n or

resp

iratio

n

Net photosynthesi

s

Gross photosynthesis

respiration

temperature

Net

pho

tosy

nthe

sis

Topt

Water deficit:Potential evapotranspiration (PET) - precipitation (PPT)

Length of growing season

Limiting nutrient availability

NPP along transect from coast of Georgia to edge of continental shelf

CE = InPn−1

×100

Consumption efficiency Energy ingested at trophic level n

Energy produced at trophic level n-1

AE=AnIn×100

Assimilation efficiency Energy assimilated at trophic level n

Energy ingested at trophic level n

PE =PnAn

×100

Production efficiency Energy produced at trophic level n

Energy assimilated at trophic level n

TLTE =Pn

Pn−1×100

Trophic level transfer efficiency

TLTE=CE×AE×PE

forest

lake

grassland

stream

Decomposer

Amino acids,Carbohydrates,

Lipids,Nucleic acidsProteins, etc.

InorganicNutrients

NO3-, SO4--, PO4---Mg, Mn, Fe, Ca, K,

etc

immobilization

H2O + CO2O2

respiration

mineralization

Dead animalor plant matter Organic C,

E, nutrients

Limiting nutrientsImmobilized

Decay rate increasedby increased contentof limiting nutrients

All nutrientsmineralized

Decay rate decreasedby increased contentof limiting nutrients

% re

mai

ning

Time

Stages of decomposition

• Early:– Autolysis– Leaching of dissolved OC, minerals– Colonization by bacteria and fungi– Decomposition of sugars and amino acids > starch

> cellulose– Population explosion of early colonizers

Stages of decomposition

• Intermediate/Late– Microorganisms specializing in using resistant

material colonize > high diversity• 1 g soil: 10,000 genetically distinct bacteria

– Degrade cellulose, complex proteins, lignins– Physical contact required (e.g., membrane surface

enzymes)

Time (weeks) Time (weeks) Time (weeks)

% O

rigin

al re

mai

ning

Nutrient dynamics during decomposition in a Scots pine forest, Sweden

Time (weeks) Time (weeks) Time (weeks)

% O

rigin

al re

mai

ning

Nutrient dynamics during decomposition in a Scots pine forest, Sweden

Terminal e- acceptor Process Gas produced

CO2 Methanogenesis CH4

NO3- Denitrification N2O; N2

NO3- Nitrate reduction NH3

SO4- - Sulfate reduction H2S

Concentrations of solutes in streams draining Hubbard Brook experimental catchments W2 (deforested and treated with herbicides in 1965) and W6 (control)